The invention relates to a plug fixing device with a piston propelled by compressed gas, comprising a plug guide, a cylinder in which the piston is mounted, a combustion chamber sleeve intended to close the chamber at the rear with a cylinder head and at the front with the piston and the cylinder, a probe for closing the chamber, a duct for injection of compressed gas into the chamber from a compressed gas cartridge and means for ignition intended to cause the gas contained in the combustion chamber to explode upon firing.
Upon firing, the gas explosion in the chamber induces a recoil force which tends to cause detachment of the device, and especially the plug guide, from the support material on which it is in abutment. Such detachment generally proves to be detrimental to the fixing of the plug which, instead of becoming embedded in the material, swerves or even breaks, in particular in the case where the material is hard, e.g. concrete.
In order to solve this problem the document EP-0 788 863 proposes a fixing device of the type defined above in which the plug guide acts as a probe for placing in abutment and for closing the combustion chamber, comprised of mechanical isolation springs disposed between the cylinder and a plug guide support fixedly attached to the plug. The cylinder is able to move forward with respect to the plug guide support against the action of the isolation springs. When the device is brought into abutment against the material, the cylinder is driven forward and compresses the springs. Then, upon firing and under the action of the recoil force, the cylinder recoils and releases the springs, the plug guide thus being kept in abutment against the material with the aid of the isolation springs.
A device of this type has a relatively complex structure. Moreover, when the device is brought into abutment, an operator must exert a force to compress the isolation spring.